Re: ld: how to force symbol resolution in shlibs on Linux

[skaller <skaller at users dot sourceforge dot net>]

On Sat, 2006-03-04 at 20:42 -0500, Daniel Jacobowitz wrote:
> On Sun, Mar 05, 2006 at 02:06:32PM +1100, skaller wrote:
> > Hi, I have a problem trying to figure out if it even possible to force
> > linkage against shared libraries to resolve all 'user' symbols on Linux.
> > 
> > The option --[no-]allow-shlib-undefined controls this but seems useless
> > because it forces resolution of gcc compiler internal symbols related
> > to the GOT etc which must remain unresolved until runtime linkage.
> 
> Sorry, you're using phrases that don't accurately describe anything.

Ok, sorry! Here is an example:


skaller@budgie:/work/felix/flx$ cat g.c
void g(){}

skaller@budgie:/work/felix/flx$ cat f.c
extern void g();
void f(){ g(); }

skaller@budgie:/work/felix/flx$ gcc -shared -fPIC -o g.so g.c
skaller@budgie:/work/felix/flx$ gcc -shared -fPIC -o f.so f.c

It failed to report an unresolved symbol. Notice that
I forgot to link f.so against g.so like I should have!

Now watch this .. various experiments to make it work:

skaller@budgie:/work/felix/flx$ gcc -Wl,--no-allow-shlib-undefined
--shared -fPIC -o f.so f.c
/lib/libc.so.6: undefined reference to `_rtld_global@GLIBC_PRIVATE'
/lib/libc.so.6: undefined reference to
`__libc_enable_secure@GLIBC_PRIVATE'/lib/libc.so.6: undefined reference
to `_rtld_global_ro@GLIBC_PRIVATE'
/lib/libc.so.6: undefined reference to `_dl_out_of_memory@GLIBC_PRIVATE'
/lib/libc.so.6: undefined reference to `_r_debug@GLIBC_2.2.5'
/lib/libc.so.6: undefined reference to `__tls_get_addr@GLIBC_2.3'
/lib/libc.so.6: undefined reference to `_dl_argv@GLIBC_PRIVATE'

Argg... mess around.. finally:

skaller@budgie:/work/felix/flx$ gcc -Wl,--no-allow-shlib-undefined
--shared -fPIC -o f.so f.c /lib/ld-linux-x86-64.so.2

No error. Hopeless!! This is all wrong. And there is no way
I am going to name the loader like that in a portable
build script!

THIS is correct:

skaller@budgie:/work/felix/flx$ cat m.c
extern void g();
int main(){ g(); }

skaller@budgie:/work/felix/flx$ gcc -o m m.c
/tmp/ccKnJ1Xk.o: In function `main':
m.c:(.text+0xa): undefined reference to `g'
collect2: ld returned 1 exit status

except of course that's a mainline static link.
I want exactly the above result, which is the only
acceptable result for almost all application links,
whether building a shared library or not -- and it's
what I get with Cygwin, MinGW, and MSVC++. So my code
can build .. and even run .. on Linux, but fail on
other platforms (it can also fail on Linux .. at run
time, which is not desirable).

There is, of course, no guarantee with shared libraries
I won't drop in an incompatible version at run time,
and break everything.

With -z defs it still doesn't work:

skaller@budgie:/work/felix/flx$ gcc -z defs -shared -fPIC -o f.so f.c
-L. -lg
/tmp/cc83tWg8.o: In function `f':
f.c:(.text+0xa): undefined reference to `g'
collect2: ld returned 1 exit status

[There is no error -- -lg is specified this time :]

-- 
John Skaller <skaller at users dot sourceforge dot net>
Async PL, Realtime software consultants
Checkout Felix: http://felix.sourceforge.net